/*
 * ProGuard -- shrinking, optimization, obfuscation, and preverification of Java bytecode.
 *
 * Copyright (c) 2002-2018 GuardSquare NV
 *
 * This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public
 * License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later
 * version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
 * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along with this program; if not, write to the Free
 * Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */
package proguard.optimize.peephole;

import proguard.classfile.*;
import proguard.classfile.attribute.*;
import proguard.classfile.attribute.visitor.AttributeVisitor;
import proguard.classfile.editor.CodeAttributeEditor;
import proguard.classfile.instruction.Instruction;
import proguard.classfile.instruction.visitor.InstructionVisitor;
import proguard.classfile.util.SimplifiedVisitor;

/**
 * This InstructionVisitor deletes blocks of code that can never be reached by regular calls or branches.
 *
 * @author Eric Lafortune
 */
public class UnreachableCodeRemover extends SimplifiedVisitor implements AttributeVisitor, InstructionVisitor {
    // *
    private static final boolean DEBUG = false;
    /*/
    private static       boolean DEBUG = true;
    //*/

    private final InstructionVisitor extraInstructionVisitor;

    private final ReachableCodeMarker reachableCodeMarker = new ReachableCodeMarker();
    private final CodeAttributeEditor codeAttributeEditor = new CodeAttributeEditor();

    /**
     * Creates a new UnreachableCodeRemover.
     */
    public UnreachableCodeRemover() {
        this(null);
    }

    /**
     * Creates a new UnreachableCodeRemover.
     * 
     * @param extraInstructionVisitor an optional extra visitor for all deleted instructions.
     */
    public UnreachableCodeRemover(InstructionVisitor extraInstructionVisitor) {
        this.extraInstructionVisitor = extraInstructionVisitor;
    }

    // Implementations for AttributeVisitor.

    public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}

    public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute) {
        // DEBUG =
        // clazz.getName().equals("abc/Def") &&
        // method.getName(clazz).equals("abc");

        // TODO: Remove this when the code has stabilized.
        // Catch any unexpected exceptions from the actual visiting method.
        try {
            // Process the code.
            visitCodeAttribute0(clazz, method, codeAttribute);
        } catch (RuntimeException ex) {
            System.err.println("Unexpected error while removing unreachable code:");
            System.err.println("  Class       = [" + clazz.getName() + "]");
            System.err.println("  Method      = [" + method.getName(clazz) + method.getDescriptor(clazz) + "]");
            System.err.println("  Exception   = [" + ex.getClass().getName() + "] (" + ex.getMessage() + ")");

            throw ex;
        }
    }

    public void visitCodeAttribute0(Clazz clazz, Method method, CodeAttribute codeAttribute) {
        if (DEBUG) {
            System.out.println("UnreachableCodeRemover: " + clazz.getName() + "." + method.getName(clazz)
                + method.getDescriptor(clazz));
        }

        reachableCodeMarker.visitCodeAttribute(clazz, method, codeAttribute);

        codeAttributeEditor.reset(codeAttribute.u4codeLength);

        codeAttribute.instructionsAccept(clazz, method, this);

        codeAttributeEditor.visitCodeAttribute(clazz, method, codeAttribute);
    }

    // Implementations for InstructionVisitor.

    public void visitAnyInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset,
        Instruction instruction) {
        if (DEBUG) {
            System.out.println(
                "  " + (reachableCodeMarker.isReachable(offset) ? "+" : "-") + " " + instruction.toString(offset));
        }

        // Is this instruction unreachable?
        if (!reachableCodeMarker.isReachable(offset)) {
            // Then delete it.
            codeAttributeEditor.deleteInstruction(offset);

            // Visit the instruction, if required.
            if (extraInstructionVisitor != null) {
                instruction.accept(clazz, method, codeAttribute, offset, extraInstructionVisitor);
            }
        }
    }
}
